Many vessels in animal bodies transport fluids from one bodily location to another. Frequently, fluid flows in a unidirectional manner along the length of the vessel. In some vessels, such as mammalian veins, natural valves are positioned along the length of the vessel and act as one-way check valves that open to permit the flow of fluid in the desired direction and close to substantially prevent fluid flow in a reverse direction, i.e., retrograde flow. These natural valves can change between open and closed positions in response to a variety of circumstances, including changes in the cross-sectional shape of the vessel and the fluid pressure within the vessel.
While natural valves may function without failure for an extended time, some may lose effectiveness, which can lead to physical manifestations and pathology. For example, venous valves are susceptible to becoming insufficient due to one or more of a variety of factors. For example, vein walls may become stretched or weakened in localized areas, affecting the ability of the valve leaflets within the affected areas to close. Furthermore, natural valve leaflets are relatively fragile and may become damaged, such as by formation of thrombus and scar tissue, which may also affect the ability of the valve leaflets to close. Ultimately, damaged venous valves may lead to venous valve insufficiency, which can produce a variety of clinical manifestations, including swelling of the lower leg, discomfort, and ulcers in the legs and ankles that are difficult to heal. Valve insufficiency patients are often unable to withstand even short periods of standing.
Current treatments for venous valve insufficiency include the use of compression stockings that are placed around the leg of a patient in a effort to force the vessel walls radially inward to restore valve function. Surgical techniques can be employed in which valves can be bypassed, repaired, such as by valvuloplasty, or replaced with artificial valves or autogenous sections of veins having competent valves. The art has recently expanded to include prosthetic valves that are implantable by minimally invasive techniques, including catheter-based deployment of self-expandable valve devices. In these devices, a graft member is typically attached to a support frame in a manner that forms some type of valve that is able to selectively open and close in response to various environmental factors, such as changes in fluid pressure, within a body vessel. For example, the graft member can be in the form of one or more leaflets that are attached to a support frame and movable between first and second positions. In a first position, the valve is open and allows fluid flow to proceed through a vessel in a first direction. In a second position, the valve is closed to prevent fluid flow in a second, opposite direction, i.e., retrograde flow. Examples of this type of prosthetic valve are described in commonly owned U.S. Pat. No. 6,508,833 to Pavcnik for a MULTIPLE-SIDED INTRALUMINAL MEDICAL DEVICE, United States Patent Application Publication No. 2001/0039450 to Pavcnik for an IMPLANTABLE VASCULAR DEVICE, and U.S. patent application Ser. No. 10/642,372, filed on Aug. 15, 2003, each of which is hereby incorporated by reference in its entirety.
The use of autogenous tissue in a valve device has the advantage of avoiding some materials-based concerns that must be taken into consideration when developing a prosthetic valve that includes a graft member formed of non-autogenous materials, such as non-natural materials and natural, non-autogenous materials. To date, however, many artisans believed that the drawbacks of using autogenous tissue in a valve device outweighed the benefits. For example, the use of autogenous tissue requires additional procedures in a treatment regimen, including harvesting of the tissue and fashioning of the tissue into a useable valve device, that many believe are too time-consuming and complicated to form the basis of a dependable treatment regimen.
As a result, there remains a need in the art for improvements relating to autogenous biomedical valves and related methods.